In the data acquisition effort in [1]}, subjects were given multiple breaks so that they could remain attentive during the task. If subjects are asked to remain attentive for more than a few minutes, a decrease in vigilance begins and attention starts to wane , , . Humans tend to become measurably inattentive in as little as 8 minutes and this is especially true during boring passive tasks in which the subject is not asked to respond , , , as is the case in [2]} and [1]}. This is why the gold standard of EEG/ERP study design suggests that blocks should be between 5-7 minutes long and separated by 1-2 minutes of rest, with additional short breaks of 15-20 seconds, 2-3 times during the block of trials . The block-designed study in [1]} followed such recommendation by using block durations of \(\sim \) 4 minutes, while the block duration in [2]}'s experiments was reported to be \(\sim \) 23 minutes (\(\sim \) 28 minutes in the video experiment), with no reported break given to subjects during that timeIt also appears that the temporal correlation was magnified in [2]} because they carried out the whole study (not only one single experiment) in a single session. Indeed, the data provided by [2]}'s authors to us during the PAMI review process, at http://upplysingaoflun.ecn.purdue.edu/~qobi/tpami2020 seems to show that some subjects underwent the entire series of experiments in a single session; e.g., by looking at file timestamps (the data comes with no metadata providing details on the recording sessions), subject 6 likely underwent experiments for more than three hours (180 minutes) consecutively.. Given the experiment duration in [2]}, it would require near super human attention to stay focused on the task designed in [2]}. This would all but guarantee that subjects would ignore the images, become inattentive and daydream, making it impossible to classify the neural data. Whereas this methodological choice would be odd and worrisome in any context, in the current research context it is unclear if this was done by design or not.
Additionally, the authors of [2]} do not report using eye gaze data for controlling experiments as we did in [1]}. Given this, they have no way to verify if subjects were looking at the images. It would be impossible to classify neural data in response to an image, if the subject had their eye's closed or they were looking away when the stimulus was presented. Knowing the subjects actually viewed the stimuli is a critical control measure that is missing in [2]}.
